A lengthy joint investigation by the Texas and California attorneys general uncovered evidence that adult and child sex trafficking victims were forced into prostitution through escort ads that appeared repeatedly on Backpage, according to Texas Attorney General Ken Paxton.

Ferrer was arrested after arriving in Houston on a flight from Amsterdam, where the company also has an office.

“Initially he’ll face charges in California for pimping and other associated crimes, but Texas will have its own investigation,” Paxton said. “Making money off the backs of innocent human beings by allowing them to be exploited for modern-day slavery is not acceptable in Texas.”

Nearly three dozen members of the Texas Attorney General’s Law Enforcement Unit participated in Ferrer’s arrest and the execution of a search warrant on the Dallas headquarters of Backpage, which is considered the largest advertiser of adult escort services in the United States.

Backpage collects fees from users who post “escort” ads, offering sex for money using coded language and nearly nude photos. The California Department of Justice’s investigation found that many of the ads for prostitution services involved victims of sex trafficking, including children under the age of 18.

The investigation was sparked by reports from media, law enforcement agencies, and the National Center for Missing and Exploited Children (NCMEC). In the last five years, NCMEC has reported an over 800% increase in reports of suspected child sex trafficking, much of it the result of online child sex trafficking.